Motor overload monitor

ABSTRACT

A motor overload monitor of the solid-state type that functions in response to closing of one or more thermal overload contacts respectively associated with a plurality of motors to provide a memory-type lamp indication of each thermal overload condition, and to drop out a power control relay common to the motors with a lamp indication of such power disconnection, and to provide a lamp indication common thereto whenever one or more overload contacts are closed that extinguishes to indicate that all of them have reset. The power control relay can be manually reset only if all overload contacts have reset to open condition and those memory-type lamp indicators can be manually reset whose respectively associated overload contacts have reset to open condition. Use of normally open thermal overload contacts allows disconnection of motors for repair without affecting operability of the rest of the system.

' United States Patent Primary Exammer-Robert L Griffin Assistant Examiner-Barry Leibowitz Attorney-Hugh R. Rather [7 2] lnventor Joel A. B. Elston Milwaukee, Wis.

c n l m 81m 67 99m 118 m a .J z vel 5H0 U 7ANC .0 06 N. d P i P mm$ AFPA 11]] 253 2247 ABSTRACT: A motor overload monitor of the solid-state type Milwaukee, Wis. that functions in response to closing of one or more thermal overload contacts respectively associated with a plurality of motors to provide a memory-type lamp indication of each [54] MOTOR OVERLOAD MONITOR thermal overload condition, and to drop out a power control 7 Claims, 1 Drawing Fig.

relay common to the motors with a lamp indication of such power disconnection, and to provide a lamp indication common thereto whenever one or more overload contacts are closed that extinguishes to indicate that all of them have reset.

The power control relay can be manually reset only if all overload contacts have reset to open condition and those memorytype lamp indicators can be manually reset whose respectively [56] References Cited associated overload contacts have reset to open condition.

UNITED STATES PATENTS Use of normally open thermal overload contacts allows disconnection of motors for repair without affecting operabilim e t S y s e h t f o t S e r e h t f o y t 333 Mill 0222 4/// 000 444 333 I M0702 Al a roe M2 l 1 P0 WEE Sl/PPL Y 6 W S o Pww $0 mi 7616 M E 0 l 7 ON L M i I l TIA L 2 m2 M m1 w M toring of the remainder of the motors and MOTOR OVERLOAD MONITOR BACKGROUND OF THE INVENTION This invention relates to the art of fault indication in multiple load device electrical systems.

Monitoring devices for certain abnormal conditions such as electrical faults or overloads have been known heretofore. In these prior art systems, it has been the usual practice to provide normally closed contacts that open in response to a fault to operate an indicator and power-disconnecting device and the like. Such normally closed contacts have generally been used to obtain fail-safe characteristics also, that is, deenergization of the relay operated by the contacts also when power fails or the voltage decreases to unsafe values. In certain applications where a plurality of motors or the like are being operated in unison requiring operation of the remainder while one or more are disconnected for repair, it has been necessary to use shorting plugs or the like for circuit continuity. While these prior systems have been useful for their intended purposes, the present invention is an improvement thereon.

SUMMARY OF THE INVENTION This invention relates to a fault condition monitor for a plurality of load devices such as a thermal overload monitor for a plural motor electrical system.

An object of the invention is to provide an improved condition-responsive monitor for a plural load electrical system.

A more specific object of the invention is to provide an improved motor overload indicator and control system for a multiple motor-driven device.

Another specific object of the invention is to provide an improved motor overload monitor for a plural motor-driven system incorporating means allowing disconnection of a motor without disturbing the operability of the remainder of the system.

Another specific object of the invention is to provide an improved memory-type motor overload monitor for a plural v motor-driven system incorporating means allowing disconnection of a motor without affecting the operability of and moniwithout sacrificing fail-safe features thereof.

Other objects and advantages of the invention will hereinafter appear.

BRIEF DESCRIPTION OF THE DRAWING The single FIG. of the drawing shows a circuit diagram of a motor overload monitor constructed in accordance with the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to the drawing, there is shown a schematic diagram of a thermal overload-monitoring circuit. As indicated by the positive and negative signals at the left side, this circuit is supplied from a control power supply such as a direct current source across supply lines SL2 and SL4. This source may be low voltage such as 12 volts or the like obtained from a commercial I IO-volt alternating-current source through a voltage-reducing transformer, a rectifier and a smoothing circuit or the like.

Supply line SL2 is a positive voltage supply line and supply line SL4 is a negative voltage supply line. A switched negative voltage conductor 6 is supplied from supply line SL4 through a normally closed contact NC of a memory indicator reset switch 8. This switch is also provided with a normally open contact NO whereby positive voltage may be connected from supply line SL2 to conductor 6 for lamp extinguishing purposes as hereinafter described.

As shown in the drawing, a plurality of thermal overload indicator circuits, one for each controlled device such as a motor, are connected across the supply lines, these circuits being indicated by the legends MOTOR M I, MOTOR M2 to MOTOR N. As will be apparent, any desired number of these indicator circuits may be connected across the supply lines although for practical reasons they are preferably arranged in multiples of four, eight and 16.

Each of these indicator circuits such as the indicator circuit for motor Ml comprises a memory-type switching device such as a semiconductor-controlled rectifier SCRl connected in series with an indicator such as a lamp L1 from positive supply line SL2 to switched negative conductor 6. A firing control circuit for SCRl extends from positive supply line SL2 through a normally open thermal overload contact 0L1, a resistor R1 and a capacitor C1 in that order to conductor 6 with the junction between the resistor and capacitor being connected directly to the gate of SCRl.

Each of these indicator circuits such as the memory indica tor circuit for motor M1 is also provided with means for operating a lamp that is common thereto. This means comprises a unidirectional diode D1 connected in its forward lowimpedance direction from the junction between contact 0L1 and resistor R1 to common conductor 10. Common indicator lamp 12 is connected between common conductor 10 and supply line SL4.

Each of the other indicator circuits individual to the other motors are provided with similar circuit components as just described in connection with the individual memory indicator circuit for motor MI. The circuit components in these other circuits are identified with similar reference characters except having suffixes 2 to 5 and N, the latter being indicative of any number.

A switching control means such as relay circuit shown at the right-hand portion of the figure is also supplied from lines SL2 and SL4. For this purpose, line SL2 is connected through the coil of relay CR, a current-limiting resistor CLR and a normally open power reset switch 14 to supply line SL4. This relay is provided with a normally open contact 1 connected across switch, 14 for self-maintaining purposes. This relay is also provided with a normally closed contact 2 in series connection with an indicator lamp 16 across supply lines SL2 and SL4 for indicating the condition of the power control relay. This relay is additionally provided with one or more output control contacts represented by normally open and normally closed contacts 3 and 4, respectively, for controlling the motor power on-off switching circuits.

The power control relay is further provided with means for controlling dropout or deenergization of the same in response to a thermal overload condition. This means comprises a memory devicesuch as a semiconductor-controlled rectifier SCRI7 connected across the power control relay coil to shunt it and cause the relay to drop out when this SCRl7 is tired.

For controlling firing of SCR17, the aforementioned common conductor 10 is connected through a resistor R17 to the gate thereof and is connected through a capacitor C17 to supply line SL4.

SCRI7 is provided with protective means in view of the inductive nature of the coil of relay CR connected across it. This means includes a capacitor 18 connected across SCR17 and a diode 20 connected across capacitor 18 and poled to conduct toward positive supply line SL2.

The operation of the system will now be described.

Overload contacts 0L1, 0L2, etc. may be of the bimetal type of the like that close in response to an excessive thermal condition in the associated motor.

Assuming that all;of the overload contacts are open, power pick up or energize relay to maintain its coil energized to allow switch 14 to be released. Contact 2 of this relay opens to extinguish lamp 16. Contact 3 of this relay closes and contact 4 thereof opens to control connection of the power to the associated motors. These motors may be of the type that drive a newspaper conveyor system or the like that requires a plurality of motors running at the same time and that can be driven temporarily by the remaining motors if one is removed for repair or replacement.

The system is now in normal condition with all lamps extinguished.

If motor M1 should overheat. contact OLl closes. As a result, current flows from supply line SL2 therethrough and through diode D1, common conductor 10 and resistor R17 into the gate of SCR17 to fire the latter into conduction. This shunts the coil of relay CR to cause the latter to drop out and reopen contacts 1 and 3 and reclose contacts 2 and 4. Contacts 3 and 4 cause the power to be disconnected from all of the motors that are in use to stop them. Current limit resistor CLR limits the current now flowing in SCR17. Capacitor C18, in combination with diode 20 across the relay coil and SCR17, limits the voltage rise across this parallel circuit, allows the inductive energy of the relay coil to be dissipated as fast as possi ble (upon SCR17 firing) without injury to the components, and prevents unwanted firing or unwanted turnofi' of SCR17.

Contact 2 of relay CR lights lamp 16 to indicate that the motor power circuit has been tripped open, and contact 1 turns SCRl7 off.

Overload contact L1 also causes current flow through diode D1 to light lamp 12 to indicate that a fault has occurred in at least one motor.

Overload contact 0L1 further causes current flow therethrough and through resistor R] into the gate of SCRl to fire this silicon-controlled rectifier into conduction. As a result, current flows from positive supply line SL2 through SCRl, lamp L1 and contact NC of switch 8 to negative supply line SL4. This causes lamp L1 to light to indicate that a thermal overload condition has occurred in motor Ml.

Resistor Rl serves the double purpose of limiting the gate current of SCRl and forming with capacitor C1 a low-pass filter and transient voltage suppressor that shunts any frequencies above about 20 Hz. from the gate of SCRl. Therefore, these gate circuits will not be operated by short duration pulses including 60 Hz. pulses. Resistors R2 to R5, RN and R17 function in a similar manner to limit gate currents and form with their associated capacitors C2 to C5, CN and C17 lowpass filters and transient voltage suppressors for similar purposes.

Diodes D1 to D and DN block current flow in the direction from conductor 10 to the gates of the SCRs to prevent sneak circuits. Thus, when the first memory circuit operates and current flows through diode D1, the other diodes prevent unwanted firing ofthe remaining SCR's.

Lamp 12 provides a discharge path for capacitors C1 to C5 and CN so that their associated SCR's can be turned off by the reset switch. A resistor may be used if lamp 12 is not desired.

It will be apparent that use of normally open contacts for the thermal overload contacts 0L1 to 0L5 and OLN permits any motor and its overload contact to be disconnected for repair or replacement without preventing operation of the remaining motors. Thus, after one motor is disconnected, the remaining motors may be restarted to operate the system on the smaller number of motors without having to install shorting plugs or the like for continuity purposes in place of the motor apparatus that was removed as would be the case if normally closed overload contacts were used. This reduces the downtime.

This use of normally open overload contacts does not sacrifice any fail-safe features obtainable with normally closed overload contacts. Normally closed contacts have been used in the prior art so that power failure, like opening thereof on overload, stops the system for fail-safe purposes. The use herein of normally open contacts that drop out a power control relay that also drops out on power failure preserves the fail-safe feature. These overload contacts are preferably operated by bimetal thermal-sensing means or the like that would appear to be as reliable for closing contacts as they are for opening contacts.

Since unidirectional voltage is used on supply lines SL2 and SL4, the silicon-controlled rectifiers provide a memory feature. For this purpose, once SCRl, for example. is rendered conducting it remains conducting until it is manually reset. Therefore, lamp Ll will remain lit as a memory of the thermal overload condition in motor M1.

The monitor is manually reset after the overload condition has been cleared. When the thermal condition has cleared, contact 0L1 automatically reopens. This causes common lamp 12 to be extinguished to indicate that all thermal conditions have cleared. Under this condition, power control relay CR can be reenergized by depressing power reset switch 14. Ifresetting is attempted by pressing switch l4 before all overload contacts have reopened, the positive voltage on conductor M) will fire SCR17 into conduction thereby preventing energization of relay CR.

The memory circuits can be reset from manual switch 8. Pressing this switch after all overload conditions have cleared, applies positive voltage through contact N0 and lamp L1 to the cathodes of SCRl and any other one that is on to turn these rectifiers off. This restores the monitor to its original inactive condition.

While the apparatus hereinbefore described is effectively adapted to fulfill the objects stated, it is to be understood that the invention is not intended to be confined to the particular preferred embodiment of motor overload monitor disclosed, inasmuch as it is susceptible of various modifications without unduly departing from the scope of the appended claims.

I claim:

I. A memory-type monitor for responding to and indicating occurrence of abnormal conditions in a plurality of controlled devices comprising:

a power supply source;

a plurality of memory circuits supplied from said source,

one for each controlled device;

each said memory circuit comprising a normally open contact operable to close in response to an abnormal condition occurring in the respectively associated controlled device;

said normally open contacts as detecting means for abnormal conditions allowing disconnection of a normally open contact when the associated controlled device is serviced without affecting operation of and monitoring of the remaining controlled devices;

each said memory circuit also comprising means responsive to closure of its normally open contact for operating an indicator and for maintaining such indicator operated even if said normally open contact reopens thereby to provide a memory indication of the abnormal condition;

power switching means energized from said source and including means adapted to control switching of power to the controlled devices;

and means common to said plurality of memory circuits and being responsive to closure of one of the abnormal-condition-responsive normally open contacts for deenergizing said power switching means to disconnect the power from the controlled devices.

2. The invention defined in claim 1, wherein said power supply source is a direct current source;

and said means in said memory circuit responsive to closure of its normally open contact for operating an indicator comprises:

a semiconductor gating device that remains conducting by current from said DC source once it is gated into conduction by closure of the associated normally open contact to maintain said indicator operated until it is reset thereby to preserve a record of the occurrence of the abnormal condition in the respectively associated controlled device.

3. The invention defined in claim 2, together with:

means common to said plurality of memory circuits and being responsive to the closure of one or more of said normally open contacts for providing an indication that an abnormal condition has occurred and being responsive to reopening of the last-closed one of said normally open contacts for providing an indication that all of said memory circuits have reset.

4. The invention defined in claim 1, together with:

manual means for resetting all of said memory circuit indicators provided all of said normally open contacts have reopened.

said power switching means including a switch for energizing said relay;

and said relay comprising means for completing a self-maintaining circuit in shunt of said switch.

7. The invention defined in claim 6, wherein said means for deenergizing said power switching means comprises:

a semiconductor gating device for closing a shunt path across said relay for deenergizing the same and for restoring its self-maintaining circuit.

I! i l i i 

1. A memory-type monitor for responding to and indicating occurrence of abnormal conditions in a plurality of controlled devices comprising: a power supply source; a plurality of memory circuits supplied from said source, one for each controlled device; each said memory circuit comprising a normally open contact operable to close in response to an abnormal condition occurring in the respectively associated controlled device; said normally open contacts as detecting means for abnormal conditions allowing disconnection of a normally open contact when the associated controlled device is serviced without affecting operation of and monitoring of the remaining controlled devices; each said memory circuit also comprising means responsive to closure of its normally open contact for operating an indicator and for maintaining such indicator operated even if said normally open contact reopens thereby to provide a memory indication of the abnormal condition; power switching means energized from said source and including means adapted to control switching of power to the controlled devices; and means common to said plurality of memory circuits and beiNg responsive to closure of one of the abnormal-conditionresponsive normally open contacts for deenergizing said power switching means to disconnect the power from the controlled devices.
 2. The invention defined in claim 1, wherein said power supply source is a direct current source; and said means in said memory circuit responsive to closure of its normally open contact for operating an indicator comprises: a semiconductor gating device that remains conducting by current from said DC source once it is gated into conduction by closure of the associated normally open contact to maintain said indicator operated until it is reset thereby to preserve a record of the occurrence of the abnormal condition in the respectively associated controlled device.
 3. The invention defined in claim 2, together with: means common to said plurality of memory circuits and being responsive to the closure of one or more of said normally open contacts for providing an indication that an abnormal condition has occurred and being responsive to reopening of the last-closed one of said normally open contacts for providing an indication that all of said memory circuits have reset.
 4. The invention defined in claim 1, together with: manual means for resetting all of said memory circuit indicators provided all of said normally open contacts have reopened.
 5. The invention defined in claim 1, together with: manual means for resetting all of the memory circuit indicators whose respectively associated normally open contacts have reopened indicating termination of abnormal conditions therein and leaving operated those memory circuit indicators whose respectively associated normally open contacts remain closed.
 6. The invention defined in claim 1, wherein said means adapted to control switching of power comprises: a relay supplied from said power supply source; said power switching means including a switch for energizing said relay; and said relay comprising means for completing a self-maintaining circuit in shunt of said switch.
 7. The invention defined in claim 6, wherein said means for deenergizing said power switching means comprises: a semiconductor gating device for closing a shunt path across said relay for deenergizing the same and for restoring its self-maintaining circuit. 